• 대한기계학회논문집B
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• 제20권11호
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• pp.3607-3619
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• 1996

Experimental and numerical studies for three-dimensional pulsatile flows are conducted to investigate the flow characteristics in the bifurcated tubes. Velocity measurements in experimental study were made by both Pulsed Doppler Ultrasound(PDU) machine and Laser Doppler Anemometer(LDA) system. Glycerin is used for experimental study. Experimental results are used to verify the results of the numerical simulation. Flow characteristics of Newtonian fluid and blood in the bifurcated tubes under the steady and pulsatlie flows are numerically investigated. Finite volume method is employed for three-dimensional numerical simulations. Blood is considered as a non-Newtonian fluid and the constitutive equation of blood is used for the numerical analysis. Numerical analyses are focused on the flow patterns for various branch angles ranging from 30.deg. to 90.deg. and diameter ratios such as 1.0, 0.8, and 0.6. Pulsatile flow characteristics of blood are compared with those of Newtonian fluid. Parameter effects on axial velocity, pressure and wall shear stress distribution along the bifurcated tubes are discussed in terms of the branch angle, diameter ratio, and Reynolds number.

• 한국전산유체공학회지
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• 제15권4호
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• pp.1-8
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• 2010

This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified $k-{\varepsilon}$ model, numerical simulations were compared with the standard $k-{\varepsilon}$ model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified $k-{\varepsilon}$ model represents intermediate characteristics between laminar and standard $k-{\varepsilon}$ model, and the modified $k-{\varepsilon}$ model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified $k-{\varepsilon}$ model were reduced about one third than low Reynolds number model including Malin's model.

• 설비공학논문집
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• 제18권4호
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• pp.370-376
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• 2006

The paper concerns an experimental study of fully developed laminar flow of a Newtonian and non-Newtonian liquid in concentric annuli with combined bulk axial flow and inner cylinder rotation. Pressure losses and skin friction coefficients have been measured for Newtonian fluid, water and non-Newtonian fluids, 0.2% aqueous of sodium carboxymethyl cellulose (CMC) and 5% bentonite solutions, when the inner cylinder rotates at the speed of $0{\sim}500$ rpm. The influences of rotation, radius ratio and working fluid on the annular flow field are investigated. And the new correlations among the skin friction coefficient, the Reynolds number and the Rossby number are presented with reasonable limits of accuracy in laminar flow regime.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1603-1612
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• 1996

The pressure loss coefficient of Newtonian and non-Newtonian fluids such as water, aqueous solutions of Carbopol-934 and Separan AP-273 and blood in the stenotic tubes are determined experimentally and numerically. The numerical analyses for flows of non-Newtonian fluids in the stenotic tubes are conducted by the finite element method. The effect of the contraction ratio and the ratio of length to diameter on the pressure drop are investigated by the experiments and numerical analysis. The pressure loss coefficients are significantly dependent upon the Reynolds number in the laminar flow regime. As Reynolds number increases, the pressure loss coefficients of both Newtonian and non-Newtonian fluids decrease in the laminar flow regime. As the ratio of length to diameter increases the maximum pressure loss coefficient increases in the laminar flow regime for both Newtonian and non-Newtonian fluids. Newtonian fuid shows the highest values of pressure loss coefficient and blood the next, followed by Carbopol solution and Separan solution in order. Experimental results are used to verify the numerical analyses for flows of Newtonian and non-Newtonian fluids. Numerical results for the maximum pressure loss coefficient in the stenotic tubes are in fairly good agreement with the experimental results. The relative differences between the numerical and experimental results of the pressure loss coefficients in the laminar flow regime range from 0.5% to 14.8%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2048-2053
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• 2003

The present study investigated the effect of the transversal vibration on the flow characteristics for non-Newtonian fluids. The effect was tested by experiment and numerical analysis. For Newtonian fluids, both of experiment and numerical analysis results showed that mechanical vibration did not affect the flow rate. For non-Newtonian fluids, however, there was significant disagreement between experiment and numerical results. The numerical results showed a negligibly small effect of vibration on the flow rate whereas experimental results showed a significant flow rate increase associated with transversal vibration. The results implied that the increased flow rate was caused not only by imposed shear rates at the wall but also by the changes of rheological characteristics due to the transversal vibration.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권1호
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• pp.1-9
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• 2007

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2% aqueous of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-500 rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• 유변학
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• 제9권4호
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• pp.140-150
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• 1997

• 한국산학기술학회논문지
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• 제12권9호
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• pp.3808-3814
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• 2011

본 연구는 열교환기의 효율적인 설계를 위하여 열교환기 내의 삼각형 단면 덕트의 비뉴톤 유체의 압력강하 및 대류 열전달률 수치해석적으로 수행하였다. 비뉴톤 유체의 구성방정식은 기존의 비뉴톤 유체 멱법칙을 보완한 수정 멱법칙 모델을 채택하였다. 덕트 내의 압력강하를 의미하는 마찰계수와 수정 레이놀즈 수의 곱은 기존 연구의 문헌치와 비교할 때 뉴톤 유체 영역과 비뉴톤 멱법칙 영역에서 각각 0.13% 및 2.85% 내에서 일치함을 보였고 비뉴톤 수정멱법칙 유체 모델의 형태를 띠는 Shear-Thinning 유체를 열교환기 내의 삼각형 단면 덕트 내에서 사용하면 뉴톤 유체보다 62%의 압력강하를 감소시켰고 12%의 대류 열전달 향상을 발생시킬 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.1-3
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• 1996

The numerical simulation techniques developed for the flows of non-Newtonian fluids including the viscoelastic fluids and the short fiber suspensions are introduced. And the causes of the numerical breakdown and the recent efforts to resolve them are presented in particular.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2008년도 Asian Magnetics Conference
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• pp.216.2-216.2
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• 2008